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Synthesis of the Special Issue: The Formation and Evolution of Ceres’ Occator Crater

Scully, Jennifer E. C. and Bowling, Timothy and Bu, Caixia and Buczkowski, Debra L. and Longobardo, Andrea and Nathues, Andreas and Neesemann, Adrian and Palomba, Ernesto and Quick, Lynnae C. and Raponi, Andrea and Ruesch, Ottaviano and Schenk, Paul M. and Stein, Nathan T. and Thomas, E. C. and Russell, Christopher T. and Castillo-Rogez, Julie C. and Raymond, Carol A. and Jaumann, Ralf (2019) Synthesis of the Special Issue: The Formation and Evolution of Ceres’ Occator Crater. Icarus, 320 . pp. 213-225. ISSN 0019-1035. http://resolver.caltech.edu/CaltechAUTHORS:20180829-103703119

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Abstract

The distinctive bright regions within Occator crater are one of the most remarkable discoveries of the Dawn mission's exploration of Ceres. The central region is named Cerealia Facula and the additional regions in the eastern crater floor are named Vinalia Faculae. Here we summarize and synthesize the results of this special issue, which aimed to identify the driving forces behind the formation of Occator and the faculae, and thus lead us to a new understanding of the processes and conditions that occurred in Ceres’ past, and potentially in its present. The investigations presented here used Dawn data, theoretical modeling and laboratory experiments to deduce the sequence of events that led to the formation of Occator, Cerealia Facula and Vinalia Faculae, which are broken into stages 1–3. Stage 1: Occator's ejecta blanket, terraces and hummocky crater floor material formed during and shortly after crater formation. These features are located in many Cerean complex craters. However, Occator also contains the lobate materials and faculae, which are unique to Occator. We interpret the lobate materials as a slurry of water, soluble salts and boulders of unmelted silicates/salts, which flowed around the crater interior before solidifying. At least portions of the lobate materials were solidified prior to the formation of the central pit, which is suggested to form via the ‘melted uplift model’ and provides insights into central pit formation across the Solar System. We propose the outer edge of Cerealia Facula formed shortly after the Occator-forming impact, via impact-induced hydrothermal brine deposition or via salt-rich water fountaining (perhaps sourced in a pre-existing reservoir). Stage 2: the majority of Cerealia Facula is located within the central pit and is interpreted to have formed later, at least ∼18 Myr after the Occator-forming impact, via multiple depositional events. The Cerealia-Facula-forming brines may have flowed out of fractures in the walls of the central pit and/or been driven to the surface by freezing of a subsurface reservoir and/or deposited via salt-rich water fountains. Further investigations are required to identify whether the formation of the majority of Cerealia Facula is driven by processes triggered by an impact, i.e. an exogenic event, or by a combination of impact-driven and endogenic processes. Cryomagmatic intrusions are suggested to uplift the crater floor, resulting in concentric floor fractures and an asymmetric dome. Injection of a similar material is proposed to inflate part of the lobate materials, giving them a hummocky texture. The resulting stresses formed fractures in the hummocky lobate material, which allowed the Vinalia-Faculae-forming brines to travel to the surface, where they ballistically erupted. The central dome within the central pit was one of the last features to form, by laccolithic intrusion, or by volume expansion from freezing of volatiles, or by extrusion of brines. Stage 3: mixing with Ceres’ average materials and/or space weathering darken the faculae over time. Cerealia Facula and Vinalia Faculae are the brightest and freshest of the bright regions identified on Ceres’ surface. Bright regions darken over time until their eventual erasure. Thus, it is likely that faculae formation has occurred throughout Ceres’ history, but that Occator's faculae are visible today because they are geologically young. Through synthesis of the studies presented in this special issue, we find that entirely exogenic driving forces, triggered by the impact, or a combination of endogenic and impact-derived forces could explain the formation of Occator and its faculae. Whether activity is impact-triggered and/or endogenic in nature is a key question for all investigations of Ceres, and future studies may favor one possibility over the other. The investigations presented in our special issue indicate Ceres is an active world where brines have been mobile in the geologically recent past. As such, Ceres is an intriguing world that we have only begun to explore.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.icarus.2018.08.029DOIArticle
ORCID:
AuthorORCID
Bu, Caixia0000-0002-4426-4425
Longobardo, Andrea0000-0002-1797-2741
Neesemann, Adrian0000-0001-6698-7651
Palomba, Ernesto0000-0002-9101-6774
Quick, Lynnae C.0000-0003-0123-2797
Raponi, Andrea0000-0003-4996-0099
Stein, Nathan T.0000-0003-2199-6751
Russell, Christopher T.0000-0003-1639-8298
Additional Information:© 2018 Published by Elsevier Inc. Received 19 January 2018, Revised 25 August 2018, Accepted 29 August 2018, Available online 29 August 2018. We would like to note that the second to fourteenth authors are listed in alphabetical order, because as the lead authors of the papers in this special issue, they contributed equally to this work. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. We thank the Dawn Flight Team at JPL for the development, cruise, orbital insertion and operations of the Dawn spacecraft at Ceres. We thank the instrument teams at the Max Planck Institute, German Aerospace Center (DLR), Italian National Institute for Astrophysics (INAF) and Planetary Science Institute (PSI) for the acquisition and processing of Dawn data. Dehydration rates for carbonates were measured at the Laboratory for Astrophysics and Surface Physics at the University of Virginia (LASP-UVa) with the assistance of G. Rodriguez Lopez and C.A. Dukes. The Dawn data upon which many of these studies are based are available on the PDS Small Bodies Node website at https://sbn.psi.edu/pds/archive/dawn.html.
Funders:
Funding AgencyGrant Number
NASA/JPL/CaltechUNSPECIFIED
Record Number:CaltechAUTHORS:20180829-103703119
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180829-103703119
Official Citation:Jennifer E.C. Scully, Timothy Bowling, Caixia Bu, Debra L. Buczkowski, Andrea Longobardo, Andreas Nathues, Adrian Neesemann, Ernesto Palomba, Lynnae C. Quick, Andrea Raponi, Ottaviano Ruesch, Paul M. Schenk, Nathan T. Stein, E.C. Thomas, Christopher T. Russell, Julie C. Castillo-Rogez, Carol A. Raymond, Ralf Jaumann, Synthesis of the special issue: The formation and evolution of Ceres’ Occator crater, Icarus, Volume 320, 2019, Pages 213-225, ISSN 0019-1035, https://doi.org/10.1016/j.icarus.2018.08.029. (http://www.sciencedirect.com/science/article/pii/S0019103518300332)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89275
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:29 Aug 2018 17:58
Last Modified:13 Feb 2019 18:59

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